Bleeding disorders, and particularly congenital or acquired deficiencies in coagulation factors, are typically treated by factor replacement. Bleeding disorders can be congenital or acquired. Coagulation disorders include hemophilia, a recessive X-linked disorder involving a deficiency of coagulation factor VIII (hemophilia A) or factor IX (hemophilia B), and von Willebrand's disease, a rare bleeding disorder involving a severe deficiency of von Willebrand factor. Hemophilia C is a milder form of hemophilia caused by a deficiency in factor XI. It is usually asymptomatic, but factor replacement therapy may be required during surgery.
Acquired coagulation disorders can be caused by inhibitory antibodies (often called “inhibitors”) against blood coagulation factors, such as Factor VIII (FVIII), von Willebrand factor, Factors (F) IX, V, XI, XII and XIII; such inhibitors can arise against exogenously infused FVIII or FIX, or in the setting of autoimmunity.
Acquired coagulation disorders may also arise in individuals without a previous history of bleeding as a result of a disease process. For example, acquired coagulation disorders may be caused by hemostatic disorders such acute trauma, administration of anticoagulants, infection, or liver disease (optionally one associated with decreased synthesis of coagulation factors), all of which are associated with decreased synthesis of coagulation factors. For example, acquired coagulation disorders may be due to disease or genetic mutations associated with increased levels of soluble thrombomodulin and fragments thereof (see Langdown J, Luddington R J, Huntington J A, Baglin T P, A hereditary bleeding disorder resulting from a premature stop codon in thrombomodulin (p.Cys537Stop). Blood. 2014 Sep. 18; 124(12):1951-6. doi: 10.1182/blood-2014-02-557538), the disclosure of which is incorporated herein by reference in its entirety).
Trauma is the leading cause of death in people younger than 45 years, with hemorrhage accounting for nearly half of these deaths within several hours (see Cothren C C, et al. Worl J Surg 2007; 31:1507-1511, the disclosure of which is expressly incorporated by reference herein). Traumatic bleeding and coagulopathy are mediated by undue activation of Protein C (PC), which in turn degrades activated (a) FV, an important clotting factor molecule (see Daniel Frith and Karim Bohi; Curr Opin Crit Care 2012, 18:631-636; and Chesebro B B, et al. 2009; Shock; 32: 659-665, the disclosures of which are expressly incorporated by reference herein). Outside of massive blood component transfusion, there is no efficacious clotting factor replacement available.
Increased risk of bleeding is also observed in patients receiving therapy with a variety of anticoagulants and there is a general unmet need for prohemostatic agents that reduce bleeding risk. Specifically, there is no effective treatment available against bleeding caused by the novel anticoagulants (NOACs) that directly inhibit Factor Xa (FXa) or thrombin [1, 2]. NOACs are increasingly prescribed for treatment and prevention of venous thromboembolism as well as prevention of strokes in the setting of atrial fibrillation, and are expected to supersede warfarin in the near future. This is because NOACs demonstrated at least equal efficacy compared to warfarin without the need of frequent patient monitoring and dose adjustments according to prothrombin times as is necessary for warfarin [3-8]. However, as with warfarin, major or clinically relevant bleeding is a consequence of treatment with NOACs, and both cause bleeding at a rate of ˜5%/year with a fatality rate of ˜5-15% [3-8]. For warfarin-induced bleeding the administration of plasma products or prothrombin complex concentrates (PCCs) is effective to achieve hemostasis [9, 10], but there are no antidotes against NOAC-induced bleeding available at current. Interventions with plasma products or PCCs in patients with NOAC-related bleeding are generally perceived as ineffective. Data are limited to in vitro studies, animal models and healthy human volunteers where plasma products or PCCs demonstrated only partial and inconsistent correction of in vitro hemostasis parameters as well as poor or no bleed reduction in animal models [2]. Moreover, intervention with rhFVIIa (NovoSeven®), approved for bleed control in patients with hemophilia and inhibitors and often used off-label for traumatic or surgical bleeding [11, 12], seems ineffective for NOAC- and warfarin-induced bleeding. Only minor corrections of in vitro hemostasis parameters were achieved with rhFVIIa (NovoSeven®) in healthy volunteers exposed to NOACs [13], and no effects on hemostasis were present in patients treated with warfarin undergoing skin biopsies [14].
Therefore, risk of bleeding and adequate prevention or control of bleeding episodes remains a major concern for these classes of drugs. The lack of clinical options to reverse bleeding associated with NOACs has spurred investigations into novel specific antidotes. As such, the reversal properties of thrombin double mutant, W215A/E217A, that shortens direct thrombin inhibitor-associated aPTT prolongation [15] and the dabigatran-specific humanized monoclonal antibody fragment aDabi-Fab were recently reported [16]. A catalytically inactive FXa that retains the ability to bind direct FXa inhibitors is in clinical development in healthy volunteers [17].
Moreover, there is currently no effective and/or approved treatment for bleeding as a common side effect of NOACs. Neither plasma products, rhFVIIa nor prothrombin complex concentrates have demonstrated clinical efficacy to rescue bleeding, but are frequently used in desperate situations absent any other treatments available.
There is also no effective treatment for other severe bleeding situations such as in hemorrhagic stroke or shock, serious injury, or perisurgically
Hemophilia is characterized by either a deficiency of FVIII or FIX, known as Hemophilia A or B, respectively. Severe hemophilia manifests with spontaneous joint, muscle and intracranial bleeding, while bleeding in mild or moderate hemophilia usually only occurs with hemostatic challenge such as trauma or surgery. Prior to the 1960s, hemophiliacs usually died as infants. With the advent of safe clotting factor preparations the median life span is now comparable to the general population (1), and the growing number of aging hemophiliacs has unmasked a new need to optimize strategies of clotting factor replacement therapies to decrease comorbidities inherent to bleeding such as burden of hemophilic arthropathy.
Conventional therapy for hemophilia A and FVIII inhibitor patients is accomplished by therapeutics like recombinant FVIII or procoagulant bypassing agents, for example FEIBA or recombinant FVIIa. Although effective, development of inhibitory antibodies which render the therapy ineffective is a common occurrence. Also, FVIIa and FEIBA as therapeutics for the treatment of FVIII inhibitor patients have quite short half-lives and so require frequent intravenous administration.
In fact, approximately 30% of hemophiliacs develop neutralizing inhibitory antibodies against exogenously administered FVIII (2), which is the most devastating complication of therapy since it leaves patients unresponsive to FVIII- or FIX-treatment. Immune tolerance induction (ITI) to eradicate inhibitors can take up to 2 years (median of 6 months) and is successful in only approximately 70% of cases (3). During this time and, life-long thereafter if ITI was not successful, patients are vulnerable to fatal bleeding, and are at high risk of developing debilitating arthropathy with poor quality of life (4).
FVIIa-based clotting factor preparations were developed to treat patients with inhibitors by rescuing bleeding through bypassing the need for intrinsic FVIIIa-, FIXa-, and FXIa-mediated thrombin amplification at the site of injury. At supraphysiological levels FVIIa accelerates thrombin generation based on direct activation of FX via tissue factor (TF)-dependent pathways or independently of TF on the surface of platelets (5, 6).
Unfortunately, treatment with FVIIa-based bypassing agents remains suboptimal and in clinical reality often unsuccessful (4, 7, 8). This makes new treatment strategies to provide more sustained thrombin formation highly desirable and have inspired investigations of several new clotting agents. These include novel FVIIa variants with increased catalytic activity and half-life (9-11), engineered FIX-molecules with enhanced ability to bind and activate FX (12), and engineered zymogen-like FX variants that become active upon engaging FVa in the prothrombinase complex (13, 14). A research group including the present inventors recently proposed “FVa activity augmentation” as another attractive alternative bypassing strategy. FVa is an important cofactor in the prothrombinase complex and enhances the rate of thrombin generation approximately 10,000-fold (15), but is also rapidly inactivated by Activated Protein C (APC) (16). Since superFVa is APC-inactivation resistant due to mutations of all three APC cleavage sites at Arg506, Arg306 and Arg679 and at glycosylation site Ser2183, the interdomain disulfide bond (His609Cys-Glu1691Cys) connecting the A2 and A3 domains (A2-SS-A3) and elimination of the glycosylation site at Asn2181 due to mutation of Ser2183Ala (16), it is an ideal molecule for “FVa activity augmentation”. This molecule demonstrated superior procoagulant properties in FVIII-deficient plasma when compared to other FVa variants and was able to control bleeding in a mouse model of Hemophilia A (von Drygalski A, et al. JTH 2014; 12:363-372), as well as in a mouse model of acquired Hemophilia A, where anti-FVIII antibodies are injected into wild-type mice to cause bleeding. Effects of superFVa were enhanced when combined with rhFVIIa.
The present invention addresses these needs and provides novel therapy and therapeutic regimens for treating conditions associated with bleeding.